First, let’s be aware of the facts about mobile devices & this perception of risk of harm:

The kind of energy sent out from mobile devices is radiofrequency & it doesn’t have the ability to damage to DNA like ionizing radiation (like an x-ray).

A number of large epidemiology studies were conducted on mobile phone use & the risk of central nervous system cancers. The studies don’t establish an association between mobile device use & the risk of central nervous system cancers.

The International Agency for Research on Cancer (IARC), part of the World Health Organization, is the principal public health authority on identifying & labeling carcinogens as such. Their working group concluded that it was probable that radiofrequency exposure from mobile devices is associated with cancer risk.

On the other hand, all of United States health agencies (Centers for Disease Control, Food & Drug Administration, & National Institute of Environmental Health Sciences) make strong statements for mobile device safety & find no link between radiofrequency energy & cancer risk.

The National Cancer Institute has made a great fact sheet on this matter.

Bottom line: As a toxicologist do I believe that there is a risk? No.

Having said that, common sense is a good thing. I’d not promote sleeping with your phone next to your head, primarily since you will benefit from uninterrupted sleep.